1. Field of Invention
The invention relates to an optical system and a display apparatus, and more particularly, to an illumination system and a projection apparatus.
2. Background
Recently, projection apparatuses using solid state light sources such as light emitting diodes (LEDs) and laser diodes have gradually held considerable market share. The luminescence efficiency of the LEDs is about 5% to 8%, and the LEDs have different spectrums available for selection, including red, green and blue spectrums. The LEDs have high spectrum peak value and narrow spectrum width and can be used as pure color light sources for projectors.
In addition, due to the luminescence limitation of the LEDs as light sources, conventional illumination systems of a projection apparatus use an exciting beam emitted by an exciting light sources, such as a laser light source, to excite a phosphor for producing light beams with higher intensity. In order to effectively excite the phosphor with the exciting beam, a cross-sectional area of the exciting beam is usually reduced, so that the exciting beam is focused to excite the phosphor. However, as conventional illumination systems using a plurality of lenses to reduce the cross-sectional area of the exciting beam, a distance is also required for reducing the cross-sectional area of the exciting beam to be suitable for exciting the phosphor, wherein the distance makes it difficult for reducing the volume of the illumination system. Additionally, when using a lens having a larger diameter to focus the exciting beam having a larger cross-sectional area, the cost of the illumination system may also be increased due to the increased cost of the lens.
US Patent Application Publication No. 20100328633 discloses a light source device including a light-source set and a first reflecting mirror set. In addition, U.S. Pat. No. 6,552,754 discloses a laser video projector.